The glass industry is quite old, and because much glass is used mechanization came relatively early to the glass industry. What is called flat glass is a strip or sheet of glass somehow removed from the glass furnace and moved horizontally through an annealing lehr to cool the glass from about 1,200.degree. to 1,400.degree.F down to perhaps 200.degree.F to remove strains from the glass by slowly cooling it under controlled heat in the lehr. The practice has long been to have a number of rolls in the lehr spaced perhaps 12, 18 or 24 inches apart to convey the strip of glass through the lehr. Customarily, these rolls were all driven by a mechanical line shaft which ran the length of the lehr and drove perhaps 100 or 200 rolls within the lehr by means of right angle gear boxes equal in number to the number of rolls. These gear boxes generally were special gear boxes to accomodate the lengthening movement of the individual rolls because of the high heat to which the rolls were subjected. Such gear boxes had to have some sliding fit to accomodate the lengthening of the rolls rather than utilizing any thrust bearing which would not permit such lengthening. As a result, the gear boxes were usually of a special design and quite costly.
Another rather recent development in the glass industry is the use of float glass, where the glass from the furnace is floated in a bath of molten metal in order to achieve a mirror-like flat bottom surface to the glass strip. It is then taken off and immediately passed to the annealing lehr for annealing. In such a case it was found that it became imperative that the rolls be ground and polished to a highly polished surface in order to not scratch or mar the float glass. Such glass was used for mirrors and in place of plate glass which previously had required grinding and polishing. For such critical uses it was imperative that the surface of glass be kept free from mar or blemishes. Also, such a float glass furnace and annealing line was something which was critical in requiring close coordination of all parts of the glass machinery line so that a continuous process was achieved with no breakdowns. Such breakdowns could be expensive in lost production and also expensive because the heat of the glass, upon a roll which was stationary rather than turning, could cause a permanent sag or set in a particular roll. Accordingly, most annealing lines were overdesigned as far as mechanical strength and requirements were concerned to minimize breakdowns and this again added to the cost of the mechanical line shaft with the special right angle gear boxes. Also, if one particular roll or pillow blocks journalling the roll should somehow become damaged and the roll stop turning, this could mark the glass so that the entire strip of glass was not useable for its intended purpose.
Also known in the glass industry were machines for the handling of discrete articles such as tumblers or other articles of glassware. For such discrete articles it is quite essential that all of the various machines handling or transferring the discrete articles be synchronized not only in speed but synchronized in phase registration. It will be appreciated that if an article is going to be transferred from one turret-like machine to a rotary transfer arm, there must be exact phase or angular registration in order to effect such transfer without breaking the glassware. Accordingly, mechanical registration was previously used, equivalent to the mechanical line shaft along the lehr.
The prior art has known mechanical line shafts for driving the rolls in an annealing lehr but due to the long length of the lehr these had the additional problems of whiplash on the long line shaft. Some patented systems used chains and sprockets to drive the rolls in the lehr whereas others attempted to use a run of a belt frictionally driving the bottom of the rolls. The prior art has also tried electrical substitutes for a mechanical line shaft, and one of the first was a variable speed DC motor driving an alternator to obtain variable frequency so that this variable frequency could energize variable speed motors. Also tried was an electrical inverter supplying a variable frequency, but this variable frequency was available only from a base speed down to about 5 hertz and, therefore, zero speed of the motors could not be achieved. Both of these systems of variable frequency, namely, the alternator or the inverter, were used to supply only wound rotor synchronous motors and these were a poor choice of motors in the high temperature ambient conditions of the typical glass plant. There was no concept of use of any alternate form of synchronous motors. The wound rotor synchronous motors relied upon current into and out of the rotor by means of brushes and some form of current collectors such as slip rings. Also, the ultra-high reliability requirements of glass plants were caused by the continuous operation of the glass furnace. The motors had to be partially enclosed, such as drip-proof or even totally enclosed, and this increased the operating temperatures of the motors.
Accordingly, for either the float glass industry or the discrete glass article manufacture, what was really wanted was some group of motors to drive conveyor mechanisms wherein the motors would make, for example, one million revolutions and the motors would still be not only in synchronization but still in the same phase.
Accordingly, the problem to be solved is how to achieve an equivalent of a mechanical line shaft or mechanical synchronization, yet effect economy in manufacture and installation of a glass machinery line along with increased reliability and ease of maintenance.
An object of the invention is to obviate the above-mentioned disadvantages of the prior art glass machinery.
Another object of the invention is to provide an electrical line shaft to control the rolls of a glass annealing lehr.
Another object of the invention is to provide a drive system for a plurality of conveying mechanisms wherein electrical synchronization is provided which will maintain not only synchronization but phase registration for all speeds from zero speed to a predetermined maximum speed.
Another object of the invention is to provide a drive system for a group of glass machines operating on discrete glass objects so that synchronization and angular registration of the machinery is accomplished.
Another object of the invention is to provide a drive system wherein rolls of an annealing lehr may be quickly moved downwardly out of contact with the strip of glass being annealed so that the roll or its drive mechanism may be replaced or repaired.
Another object of the invention is to provide a drive system for a plurality of rolls in an annealing lehr with each roll deiven by a squirrel cage synchronous motor and a right-angle gear drive, both supported on the roll itself.